Continuous process for production of nicotinic acid



P 1959 G. M. ILLICH, JR 2,905,688

commuous PROCESS FOR PRODUCTION OF mcomuc ACID FiledOct. 4. 1954 2! i I E] I31 T k 'T' *0 II 3 IT "|'z f I i l8 19 15 Irv/enfor- United States Patent CONTINUOUS PROCESS FOR PRODUCTION OF NICOTINIC ACID George M. Illich, Jr., Lake Forest, 111., assign'or to Abbott Laboratories, Chicago, 111., a corporation of Illinois Application October 4, 1954, Serial No. 459,942

10 Claims. (Cl. 260-2955) This invention relates to an improved method of producing acidic compounds from an alkyl substituted heterocyclic nitrogen compound and more particularly to a method of manufacturing nicotinic acid by the continuous oxidation of a B-alkyl substituted heterocyclic nitrogen compound.

It is known that certain heterocyclic nitrogen compounds, such as Z-methyl-S-ethyl pyridine can be readily oxidized to nicotinic acid or other heterocyclic nitrogen products under oxidizing conditions. The known methods of efliecting the oxidation of a lower alkyl substituted heterocyclic nitrogen compound including the B-lower alkyl substituted and the a, 6-di-lower alkyl substituted heterocyclic nitrogen compounds ot nicotinic acid, however, have heretofore generally involved the use of large excesses of oxidizing acids, usually in combination with an oxidizing catalyst, and these methods have not been adaptable to the more economical and less hazardous continuous operating conditions.

It is therefore an object of the present invention to provide a more economical and less hazardous process of producing acidic compounds from a heterocyclic nitrogen compound having a lower alkyl substituent in the p-position.

It is also an object of the present invention to provide an improved continuous process of producing acidic compounds from B-lower alkyl substituted heterocyclic nitrogen compounds.

It is a still further object of the invention to provide an improved and more economical method of producing nicotinic acid from a fl-lower alkyl substituted heterocyclic nitrogen compound.

An additional object of the present invention is to provide an improved process for the continuous oxidation of Z-methyl-S-ethyl pyridine to nicotinic acid.

Other objects of the invention will be apparent from the detailed description and claims to follow.

The foregoing objects and advantages of the present invention will be better understood by reference to the following specification when taken in conjunction with the accompanying drawing wherein the single figure is a schematic flow diagram of the herein disclosed process. It has been discovered that the foregoing objects are achieved by continuously oxidizing a heterocyclic nitrogen compound substituted in the ,8-position with a lower alkyl group comprising between about 1 and 4 carbon atoms by continuously passing said nitrogen compound admixed with a stoichiometric amount of aqueous nitric acid through a high pressure reaction zone having a temperature ranging between about 240 and 300 C. under the conditions disclosed herein. In contrast with the oxidation processes disclosed heretofore, the present reaction proceeds smoothly without any rapid rise in temperature or localized overheating, and at a rate sufficient to permit continuous flow through a high pressure reaction zone.

- In carrying out the above continuous reaction, the optimum operating conditions are dependent primarily upon the interaction of the conditions of pressure, temperature, and the space velocity of the reactants within the reaction zone. In general, it has been found that as the pressure and the temperature within the reaction zone increases, the yield increases within the pressure range between about 500 and 1500 lbs. per square inch and within the temperature range of about 240 to 300 C. It has also been found that an increase in the rate of flow of the reactants through the reaction zone (space velocity) results in an increased yield of the desired product. Thus, with a space velocity of 6.7 liters per hour per liter of reactor volume the yield of nicotinic acid obtained by continuously oxidizing Z-methyl-S-ethyl pyridine at a temperature of'253 C. at a pressure of 750 lbs. per square inch is 64% by weight whereasv a yield of only 51% by weight nicotinic acid is obtained by using a space velocity of 1.5 liters per hour per liter of reactor volume at a temperature of 258 C. at a pressure of 750 lbs. per square inch. When a space velocity in excess of 6.7 liters per hour per liter of reactor volume is used with an accompanying increase in yield, it is necessary to employ sufiicient cooling to maintain the temperature of the reaction zone within the specified maximum operating limits. The continuous production of nicotinic acid by the oxidation of 2-methyl-5-ethyl pyridine with nitric acid in accordance with the present invention can be most effectively carried out at a reaction temperature of at least about 270 C. and not substantially above 300 C. and at a pressure of at least about 1250 lbs. per square inch with a space velocity of at least about 5.5 liters per hour per liter of reactor volume, since under thelatter operating conditions the reaction is autogenous, proceeding continuously and smoothly without the addition of heat to the reaction system. A higher space velocity accompanied by increased cooling of the reactor will result in a somewhat increased yield.

While the process of the present invention can be carried out by employing a variety of apparatus familiar to those skilled in the art, it is possible to conveniently effect the reaction of the present invention by using the following apparatus shown schematically in the drawing which comprises a stainless steel reactor tube 10 which has an internal diameter of about 1.5 and about 36 inches in length fitted with stainless steel end closures and screw cap fittings, each having an axial opening therethrough for accommodating the outwardly extending portion of the end closures. A strip heater 11 controlled by a variable transformer (not shown) is mounted on the reactor tube to provide the heat necessary to initiate the oxidation reaction. A stainless steel regenerative heat exchanger bayonet type inlet tube 12 having an external diameter of about A" extends through one end closure to a point about one-third below the upper end of the reactor tube and through which the aqueous nitric acid solution of the fi-substituted heterocyclic nitrogen compound is introduced and heated to reaction temperature while passing therethrough. Suitable connections 13, 14 extend through the said end closures through which the reaction products are conveyed to a vapor-liquid separator 15 which also serves as a ballast tank. The product is withdrawn from the reactor into a suitable receiver 16. The gaseous reaction products are vented from the said separator through suitable pressure control apparatus including a pressure control device 17. The vapor-liquid separator is a duplicate of the reactor tube except that it has no strip heater mounted thereon and it is also provided with an armored sight glass 18 to facilitate determining the volume of product in the reactor and separator. The system is also provided with a thermowell 19, a temperature recorder 20, and a pressure transmitter 21 to facilitate operating the apparatus by remote control. An air compressor 22 3 providing high pressure air can be connected with the reactor to pressurize the said reactor tube with air at the start of the reaction after which partially reacted feed is pumped into the reactor tube through the regenerative heat exchanger tube, although the compressor is not essential as the necessary initial pressure can be obtained by partially pressurizing the reactor with nitrogen and adding prereacted material or by the addition 'of partially reacted material and heating to reaction temperature whereupon the gases evolved are allowed to accumulate until the desired pressure is reached. The reactor tu-be referred to herein is described in greater detail in the co=pending application, Serial No. 457,020, filed September 20, 1954, now Patent No. 2,822,392.

The following specific examples are set forth for the purpose of illustrating the present invention and should not be construed to limit the invention to the precise ingredients and proportions shown.

Example I A feed solution containing nitric acid and 2-methyl-5- ethyl pyridine having a molal ratio of 6 mols nitric acid to tract of Z-rnethyI-S-ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 '(70 weight percent) with 8.52 parts by weight of water and then mixing with 1 part 2-metl1'yl-5-ethyl pyridine having a density of 0.922. The foregoing feed mixture was pumped into the reactor which was preheated to a maximum temperature of 253 C. and a pressure of 75 lbs. per square inch at a rate of 3.08 liters per hour. A heat input of 0.67 kilowatt was required to maintain the reaction at a temperature of substantially 253 C. A yield of 64.2% nicotinic acid having a melting point of 234-237" C. was obtained by fractional isol-ation of the product withdrawn continuously from the reactor into the product receiver.

Example II A feed solution containing nitric acid and 2-me'thyl-5- ethyl pyridine having a molal ratio of 6 mols nitric acid to 1 mol of Z-methyI-S-ethyl pyridine was prepared by diluting 4.48 parts by Weight nitric acid having a density of 1.42 (70 weight percent) with 8.52 parts by weight of water and then mixing with 1 part Z-methyI-S-etliyl pyridine having a density of 0.922. The foregoing feed mixture was pumped into the reactor at a temperature of 244 C. and a] pressure of 750 lbs. per square inch at a rate of 6.3 liters per hour. A heat input of 0.63 kilowat was required to" maintain the reaction at a temperature of substantially 244 C. A yield of 56.2% nicotinic acid having a'niel'tin'g point of 234237 C. was obtained by fractional 4 to 1 mol of Z-methyl-S-ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 8.52 parts by weight water and then mixing with 1 part Z-methyl-S-ethyl pyridine having a density of 0.922. The foregoing feed mixture was pumped into the reactor at a temperature of 261 C. and a pressure of 1000 lbs. per square inch at a rate of 6.5 liters per hour, A heat input "of 0.55 151ewatt was required to maintain the reaction at a temperature pf substantially 261 C. A yield of 65.1% nicotinic acid having ainelting point of-234 237 C. was obtained by fractional isolation of the product stream withdrawn continuously from the reactor into the p'roduct receiver.

Example V A feed solution containing nitric acid and Z-methyl-S- ethyl pyridine having a molal ratio of 6 mols nitric acid to 1 mol of 2-methyl-5 ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 8 .52 :parts by weight water and then mixing with 1 part 2-me'thyl-5-ethyl pyridine having a density of 0.922. The foregoing feed mixture was pumped into the reactor at a temperature of 242 'C. and a pressure of 750 lbs. per square inch at a; rate of 6.3 liters per hour. A heat input of 0.30 kilowatt was required to maintain therea'ction at a ternperature of substantially 242 C. A yield of 62.5%

V nicotinic acid having a melting point of 234-237" C. was

obtained by fractional isolation of the product stream withdrawn continuously from the reactor into the product receiver.

Example VI A feed solution containing nitric acid and z-memyl-sethyl pyridinehaving a molal ratio of 6 mols nitric acid to 1 mol of 2-methyl-5-ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 8.52 parts by weight water and then mixing with 1 part 2-methyl-5-ethyl yre dine having a density of 0.922. The foregoing feed mix ture was pumped into the reactor which was preheated to a rnaximum temperature of 271 C. and a pressure of 1250 1bs. per square inch at a rate of 6.46litersper hour. The heat of reaction is sufiicient to maintain the isolation of the product withdrawn continuously from the V reactor into the product receiver;

Example III Afeed solution containing nitric acid and Z-methyl-S- ethylpyridine having a molal ratio of 6 mols nitric acid to l mol of Z-methyl-S-ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 3.52 parts by weight water and then mixing with 1 part 2-n1ethyl-5-ethyl pyridine having a density of 0.922. The foregoing feed mixture was pumped into the reactor which was preheated to a maximum temperature of 269 C. and apressure of I000 lbs. per square inch ata rate of 4.96 liters per hour. A heat input of 0.67 kilowatt was required to maintain the reactionata temperature ofsubstantially 269' e, A- yield oi 56% nicotinic acid having a melting point 9f 234-237 C. was obtained by'fractional isolatiohof the product stream withdrawnc'ontinuously from the reactor into theproduct receiver.-

I Example IV A feed splution containing acidand2-methyl-5 ethyl pyiidine having a molal ratio of 6 mols nitric acid In reactants at a temperature of substantially 271 C. A yield of 70.7% nicotinic acid having a melting point of 234-237" C. was obtained by fractional isolation of the product stream withdrawn continuously from the separator into the product receiver.

Example VII 1 A feed solution containing nitric acid and 2-methyl-5- ethyl pyridine having a molal ratio of 6 mols nitric acid to 1 mol of 2-methyl-5-ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 8.52 parts by weight Water and then mixing with 1 part Z-methyl-S-ethylpyrh dine having a density of 0.922. The foregoing feed mix ture was pumped into the reactor which was preheated to a maximum temperature of 285 C. and a pressure oi 1500 lbs. per square inchat a rate of 645' liters .per hour. The heat of reaction is suflicient to maintain the reactants at a temperature of substantially 285 C. A yield of 72.2% nicotinic acid having a melting point of 234237 C. was obtained by fractional isolation of the product stream withdrawn continuously from the separater into the product receiver.

Example V111 A feed solution containing nitric acid and,2-methyl-5 ethyl pyridine having a molal ratio of 6 mols nitric acid to 1 mol of Z-methyl-S-ethyl pyridine was prepared by diluting 4.48 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 8.52 parts by weight water and thenmixingwith 1 part.Z-methyhS-ethylpyridine having a denity of 0.92 The foregoing feed mixture was pumped into the reactor which was preheated to a maximum temperature of 295 C. and a pressure of 1500 lbs. per square inch at a rate of 5.45 liters per hour. The heat of reaction is sufiicient to maintain the reactants at a temperature of substantially 295 C. A yield of 68.2% nicotinic acid having a melting point of 234- 237 C. was obtained by fractional isolation of the product stream withdrawn continuously from the separator into the product receiver.

Example IX A feed solution containing nitric acid and fi-picoline having a molal ratio of 2 mols nitric acid to 1 mol of picoline was prepared by diluting 1.94 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 2.66 parts by weight Water and then mixing with 1 part fi-picoline having a density of .961. The foregoing feed mixture was pumped into the reactor which was preheated to a maximum temperature of 270 C. and a pressure of 1250 lbs. per square inch at a rate of 6.0 liters per hour. A yield of 65% nicotinic acid having a melting point of 234237 C. was obtained by fractional isolation of the product stream withdrawn continuously from the reactor into the product receiver.

Example X A feed solution containing nitric acid and 3-ethyl pyridine having a molal ratio of 4 mols nitric acid to 1 mol of 3-ethyl pyridine was prepared by diluting 3.36 parts by weight nitric acid having a density of 1.42 (70 weight percent) with 5.34 parts by weight water and then mixing with 1 part 3-ethyl pyridine having a density of .959. The foregoing feed mixture was pumped into the reactor which was preheated to a maximum temperature of 275 C. and a pressure of 1250 lbs. per square inch at a rate of 6.5 liters per hour. A yield of 68% nicotinic acid having a melting point of 234-237 C. was obtained by fractional isolation of the product stream withdrawn continuously from the reactor into the product receiver.

In the process of the present invention the regenerative heat exchange between the incoming feed and the reaction mixture contributes greatly to the efiiciency of the process, since it eliminates the necessity of adding heat to the fresh reactants in order to raise the energy level thereof to reacting temperatures once the reaction is initiated and thus permits the reaction to proceed without the addition of any heat to the reactor. In larger reactors, if desired, more than one regenerative heat exchanger tube can be used. Also, in the foregoing examples, it has been found desirable to insulate the reactor in order to conserve heat.

While the examples employed to illustrate the present invention have been limited to the use of Z-methyl-S-ethyl pyridine, fi-picoline, and 3-ethyl pyridine, it should be understood that other lower alkyl and alkylene pyridines which have the alkyl or alkylene group substituted at least in the B-position and including a,fi-lower alkyl substituted pyridines wherein the lower alkyl and alkylene groups contain between 1 and 4 carbon atoms can be used to produce nicotinic acid under the conditions outlined in the preceding examples and in accordance with the present invention. For example, 3-propyl pyridine, 3-allyl pyridine, 3-n-butyl pyridine, 3,6dimethyl pyridine, 2-ethyl-5- methyl pyridine, and 2,3,6-trimethyl pyridine. Quinoline and nicotine can also be employed in the present continuous process.

Others may readily adapt the invention for use under various conditions of service, by employing one or more of the novel features disclosed or equivalents thereof. As at present advised with respect to the apparent scope of my invention, I desire to claim the following subject matter.

I claim:

1. A continuous process of preparing nicotinic acid which comprises passing a feed mixture of nitric acid and a heterocyclic nitrogen compound substituted with a lower alkyl group at least in the fi-position in stoichiometrically equivalent amounts continuously at a flow rate of at least about 5.5 liters per hour per liter of reactor volume through a reaction zone in which the reactants are maintained at a pressure of at least about 1250 pounds per square inch and at a temperature of at least a minimum of about 270 C. and not substantially above about 300 C.; said reaction being autogenous after initially preheating the reactants to the said minimum temperature and thereafter passing the said feed mixture in countercurrent heat exchanging contact with the reaction products.

2. A continuous process substantially as described in claim 1 wherein the said fiow rate is between about 5.5 and 7.0 liters per hour per liter of reactor volume.

3. A continuous process substantially as described in claim 1 wherein the said heterocyclic nitrogen compound is an a,fl-di-substituted pyridine compound.

4. A continuous process substantially as described in claim 1 wherein the said nitrogen compound is a pyridine compound which is substituted in at least the 3-position with a lower alkyl group.

5. A continuous process as in claim 4 wherein the said pyridine compound is 3-methyl pyridine.

6. A continuous process as in claim 4 wherein the said pyridine compound is 3-ethyl pyridine.

7. A continuous process as in claim 4 wherein the said pyridine compound is 3-propyl pyridine.

8. A continuous process as in claim 4 wherein the said pyridine compound is Z-methyl-S-ethyl pyridine.

9. A continuous process for producing nicotinic acid which comprises passing a feed mixture of nitric acid and 2-methyl-5-ethyl pyridine in stoichiometrically equivalent amounts continuously at a fiow rate of about 6.5 liters per hour per liter of reactor volume through a reaction zone in which the reactants are maintained at a pressure of about 1500 pounds per square inch and at a temperature of about 285 C.; said reaction being autogenous after initially preheating the feed mixture to a temperature of 285 C. and thereafter passing the said feed mixture in countercurrent heat exchanging contact with the reaction products.

10. A process for the production of nicotinic acid by reaction of a 2,5-dialkyl pyridine and nitric acid which comprises reacting the 2,5-dialkyl pyridine with nitric acid in an aqueous solution at a temperature between about 240 C. and 300 C. and at a pressure above about 750 pounds per square inch and above the vapor pressure of the aqueous solution of nitric acid at the temperature employed.

References Cited in the file of this patent UNITED STATES PATENTS 2,394,650 Zimmerli Feb. 12, 1946 2,522,163 Cislak et al Sept. 12, 1950 2,524,957 Burrows et a1. Oct. 10, 1950 2,647,141 Cavanaugh et al July 28, 1953 2,657,207 Herring Oct. 27, 1953 2,694,070 Martin Nov. 9, 1954 2,702,802 Aries Feb. 22, 1955 FOREIGN PATENTS 892,871 France Ian. 17, 1944 1,054,523 France Oct. 7, 1953 

10. A PROCESS FOR THE PRODUCTION OF NICOTINIC ACID BY REACTION OF A 2,5-DIALKYL PYRIDINE AND NITRIC ACID WHICH COMPRISES REACTING THE 2,5-DIALKYL PYRIDINE WITH NITRIC ACID IN AN AQUEOUS SOLUTION AT A TEMPERATURE BETWEEN ABOUT 240* C. AND 300* C. AND AT A PRESSURE ABOVE ABOUT 750 POUNDS PER SQUARE INCH AND ABOVE THE VAPOR PRESSURE OF THE AQUEOUS SOLUTION OF NITRIC ACID AT THE TEMPERATURE EMPLOYED. 